Interpretive Summary: Invasive species of weedy plants cause the U.S. and other countries hundreds of million dollars in direct losses and management costs associated with their control. The introduction of host-specific plant-feeding insects as biocontrol agents has proven to be a successful and environmentally benign approach to weed management. This study formally describes three new species of host-specific plant-feeding flies that attack paperbarks and eucalypt tree species. Adult and larval morphologies are described and illustrated. Host-use patterns and geographic distributions are clarified. This information will be used by biocontrol scientists, taxonomists, and evolutionary biologists.

Technical Abstract:
Three Fergusonina (Diptera: Fergusoninidae) flies are described from terminal leaf bud galls on Eucalyptus L'Hér. from south eastern Australia. Fergusonina omlandi Nelson and Yeates sp. nov. is the third fly from the genus Fergusonina to be described from the Eucalyptus pauciflora Sieb. ex Spreng. (Snow Gum) species complex; the other two occur in sympatry at higher elevations. Fergusonina omlandi sp. nov. can be distinguished from the high elevation snow gum species by differences in adult size and markings on the mesonotum. The other new species, Fergusonina williamsensis Nelson and Yeates sp. no. and Fergusonina thonhilli Nelson and Yeates sp. nov. are the first flies to be described from Eucalyptus baxteri (Benth.) Maiden & Blakely and Eucalyptus dalrympleana Maiden, respectively. These two species can be distinguished from other described species of Fergusonina by host specificity, adult colour, setation and larval dorsal shield morphology.